Image signal processing apparatus and processing method

ABSTRACT

The present invention provides an image signal processing apparatus and a method thereof in which each of the fields forming the unit-frame is specified, with respect to the inputted image signal, based on a difference value calculated in signal level between a detected pixel in a current field and a detected pixel at the same position in a field which comes one frame behind the current field, a motion vector for a field which comes two frames behind the current field is detected, with respect to the detected pixel in the current field, the detected pixel is shifted, with respect to the specified first field, in a direction opposite to the motion vector within the range of the detected motion vector, the detected pixel is shifted, with respect to the specified fourth field, in a direction along the motion vector, and the detected pixels is shifted, with respect to the specified second and third fields, so as to make the pixels gradually closer to the pixel position shifted with respect to the fourth field, in the consecutive order of the fields from the first field, in the direction along the motion vector or in the direction opposite to the motion vector.

TECHNICAL FIELD

The present invention relates to an image signal processing apparatuswhich shifts the position of each detected pixel of image signals whichare generated by performing double-speed conversion on images subjectedto telecine conversion and consist of unit-frames each formed of 4fields, and an image processing method thereof.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2001-380765 filed Dec. 13,2001, the entire contents of which are incorporated herein by reference.

BACKGROUND ART

As a conventional scanning system used for TV broadcasting, an interlacescanning system which scans every other horizontal scanning lines hasbeen widely used. In this interlace scanning system, every frame imageis formed of a field image consisting of odd-numbered scanning lines anda field image consisting of even-numbered scanning lines, to suppressscreen flicker disturbance which causes the entire screen to flicker,thus preventing deterioration of the screen quality.

The interlace scanning system has been adopted as a standard system fortelevision in countries throughout the world. For example, according toPAL (Phase Alternation by Line) system in European televisionbroadcasting, the field frequency is 50 Hz (frame images: 25frame/second, field images: 50 fields/second).

In particular, the PAL system conventionally adopts a double-speed fieldfrequency system in which the field frequency of inputted image signalsis converted to be doubled from 50 Hz to 100 Hz, by performing aninterpolation processing or the like, expecting further suppression ofthe screen flicker disturbance.

FIG. 1 is a block diagram showing a double-speed field conversioncircuit 5 using the double-field-frequency system. The double-peed fieldconversion circuit 5 is integrated in a television receiver 6 which hasan input terminal 61, a horizontal/vertical deflection circuit 62, and aCRT 63. This double-speed field conversion circuit 5 has a double-speedconverter 51, and a frame memory 52.

The double-speed converter 51 writes image signals of 50 fields/secondaccording to the PAL system inputted from the input terminal 61 into theframe memory 52. Also, the double-speed converter 51 reads the imagesignals written in the frame memory 52, at a speed twice higher than thewriting speed. Thus, the frequency of the image signals of 50fields/second is converted to a double frequency, so that image signalsof 100 fields/second can be generated.

The double-speed converter 51 outputs the image signals subjected to thedouble conversion to the CRT 63. The CRT 63 displays the inputted imagesignals on the screen. Horizontal and vertical deflection of the imagesignals in the CRT 63 is controlled based on a horizontal/verticalrectangular wave which is generated by the horizontal/verticaldeflection circuit 62 and has a frequency which is twice that of theinputted image signals.

FIGS. 2A and 2B show a relationship between each field and pixelpositions with respect to image signals before and after thedouble-speed conversion. In each figure, the abscissa axis representstime, and the ordinate axis represents the position of each pixel in thevertical direction. The image signals indicated by white circle marks inFIG. 2A are interlace image signals of 50 fields/second before thedouble-speed conversion, and the image signals indicated by black circlemarks in FIG. 2B are interlace image signals of 100 fields/second afterthe double-speed conversion.

In the image signals shown in FIG. 2A, fields f₁ and f₂ are signalsgenerated from one single unit-frame of a film. Likewise, fields f₃ andf₄ constitute one single unit-frame. Since these image signals areinterlace image signals, the pixel positions in the vertical directiondiffer between adjacent fields. Therefore, it is impossible to create anew field between every two adjacent fields, maintaining thecharacteristics of interlacing.

Hence, as shown in FIG. 2B, two fields f₂′ and f₁′ are newly generatedbetween the fields f₁ and f₂. No new fields are generated between thefields f₂ and f₃ but two new fields f₄′ and f₃′ are generated betweenthe fields f₃ and f₄. That is, one unit-frame is formed of four fieldsforming two frames.

In some cases, those newly generated fields f₁′, f₂′, . . . are obtainedby using a median filter or the like, supposing that each pixel value isan intermediate value among three pixels surrounding each pixel. Thenewly generated fields f₁′, f₂′ . . . have the same contents as thefields f₁, f₂, . . . , respectively.

Specifically, the double-speed field conversion circuit 5 provides partsin each of which two new fields are generated and parts in each of whichno new fields are generated, alternately among fields of image signalsbefore the double-speed conversion. The number of screen images per unittime can thus be increased so that the screen flicker disturbance aspreviously described can be suppressed.

In order to watch a cinema film consisting of still images of 24unit-frames/second on an ordinary TV set, television-to-cinemaconversion (which will be hereinafter referred to as telecineconversion) is carried out to attain interlace television signals. FIGS.3A and 3B show a relationship between each field and an image positionin case where an image moves in the horizontal direction, with respectto the image signals after the telecine conversion. The abscissa axisrepresents the position of the image in the horizontal direction, andthe ordinate axis represents time. In the image signals before thedouble-speed conversion shown in FIG. 3A, the fields f₁ and f₂ form onesingle unit-frame, so that the image is displayed at the same position.This image moves in the horizontal direction (to the right side) as thefield shifts to the field f₃. Since the field f₄ forms part of the sameunit-frame as the field f₃, the image is displayed at the same positionas in the field f₃.

If image signals shown in FIG. 3A after the telecine conversion aresubjected to the double-speed conversion according to the double-speedfield frequency system, as shown in FIG. 3B, an equal image is displayedat an equal position in the fields f₁, f₂′, f₁′, and f₂ forming onesingle unit-frame. Similarly, as equal image is displayed at an equalposition in the fields f₃, f₄′, f₃′ and f₄ forming one singleunit-frame.

The image signals subjected to the double-speed conversion after thetelecine conversion are displayed at one equal position from the fieldf, to the field f₂ as shown in FIG. 3B. On the other side, the signalsgreatly move in the horizontal direction when the field shifts from f₂to f₃. In particular, the image signals after the double-speedconversion form fields regularly at a cycle of one field per 1/100second. Therefore, a time band in which an image moves is shorter thananother time band in which an image stands still. When a program isactually watched by a CRT, motions of images look discontinuous. Toeliminate such discontinuity in motions, for example, a screen image isdivided into blocks each consisting of predetermined pixels, based on ablock matching method, and a motion vector is obtained by evaluatingsimilarity in units of blocks. The motion is corrected by shifting pixelpositions for every block in accordance with the obtained motion vector.

Suppose, however, a case that motions take place in two directions on atelevision screen T, as shown in FIG. 4. That is, an image A of anobject moves to the left side in the direction of an arrow X₁ in thefigure while a background B moves to the right side in the direction ofan arrow X₂ in the figure. In this case, the direction of a motionvector as described above cannot be detected correctly, and therefore,the discontinuity in motions of images as described above cannot beelirninated. The reference symbol C in FIG. 4 denotes a block to performthe block matching described above.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a novel image signalprocessing apparatus and a method thereof capable of solving problemsinvolved by an image signal processing apparatus as described above andthe method thereof in which double-speed conversion is performed onimages subjected to telecine conversion.

Another object of the present invention is to provide an image signalprocessing apparatus and a method thereof capable of smoothening motionswhile suppressing screen flicker disturbance, with respect to imagesignals generated by performing double-speed conversion on imagessubjected to telecine conversion, even in images of wide variations suchas an image which includes motions in two directions in one singleblock.

According to the present invention, there are provided an image signalprocessing apparatus and a method thereof, in which image signals whichare generated by performing double-speed conversion on images subjectedto telecine conversion and consist of unit-frames each formed of fourfields are inputted, and the respective fields are specified on thebasis of calculated difference values in pixel signal levels. Thepositions of detected pixels are shifted such that the pixel position inthe first field thus specified is shifted in a direction opposite to amotion vector, the pixel position in the fourth field also specified isshifted in the motion vector, and the pixel positions in the second andthird fields also specified are shifted to be gradually closer to thepixel position shifted in the fourth field as the fields come later fromthe first field.

Specifically, an image signal processing apparatus according to thepresent invention is inputted with an image signal which is generated byperforming double-speed conversion on an image subjected to telecineconversion and which is formed of unit-frames each including four fieldsof first and successive second to fourth fields, each of the unit-framestaring from the first field, comprising: a sequence detector whichcalculates a difference value in signal level between a detected pixelin a current field and a detected pixel at the same position in a fieldwhich comes one frame behind the current field, with respect to theinputted image signal, and specifies each of the fields forming theunit-frame, based on the difference value; a motion vector detectorwhich detects a motion vector for a field which comes two frames behindthe current field, with respect to the detected pixel in the currentfield; and an image controller which shifts the positions of thedetected pixels of the image signal within the fields specified by thesequence detector, respectively, in accordance with a vector quantity ofthe motion vector, wherein the image controller shifts the detectedpixel, with respect to the specified first field, in a directionopposite to the motion vector, the image controller shifts the detectedpixel, with respect to the specified fourth field, in a direction alongthe motion vector, and the image controller shifts the detected pixels,with respect to the specified second and third fields, so as to make thepixels gradually closer to the pixel position shifted with respect tothe fourth field, in the consecutive order of the fields from the firstfield, in the direction along the motion vector or in the directionopposite to the motion vector.

Specifically, an image signal processing method according to the presentinvention comprises the steps of: inputting an image signal which isgenerated by performing double-speed conversion on an image subjected totelecine conversion and which is formed of unit-frames each includingfour fields of first and successive second to fourth fields, each of theunit-frame staring from the first field; specifying each of the fieldsforming the unit-frame, with respect to the inputted image signal, basedon a difference value calculated in signal level between a detectedpixel in a current field and a detected pixel at the same position in afield which comes one frame behind the current field; detecting a motionvector for a field which comes two frames behind the current field, withrespect to the detected pixel in the current field; shifting thedetected pixel, with respect to the specified first field, in adirection opposite to the motion vector; shifting the detected pixel,with respect to the specified fourth field, in a direction along themotion vector; and shifting the detected pixels, with respect to thespecified second and third fields, so as to make the pixels graduallycloser to the pixel position shifted with respect to the fourth field,in the consecutive order of the fields from the first field, in thedirection along the motion vector or in the direction opposite to themotion vector.

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description taken inconjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a double-speed field conversioncircuit to which a double-speed field frequency system is applied;

FIGS. 2A and 2B show a relationship between each field and pixelpositions with respect to image signals before and after thedouble-speed conversion;

FIGS. 3A and 3B show a relationship between each field and an imageposition in case where an image moves in the horizontal direction;

FIG. 4 is a view for explaining an image of a variation in which onesingle block includes motions in two directions;

FIG. 5 is a partial block circuit diagram showing an image signalprocessing apparatus to which the present invention is applied;

FIGS. 6A and 6B show a relationship between each field and pixelpositions before and after double-speed conversion in the double-speedfield conversion circuit;

FIG. 7 shows a relationship between each field and an image position incase where an image moves in the horizontal direction;

FIG. 8 is a view for explaining a method of detecting a sequence by asequence detector;

FIG. 9 is a view for explaining a method of shifting an image in eachfield;

FIG. 10 is a view showing a result of shifting an image in each field;

FIG. 11 is a view for explaining a method of shifting respective imagesin the first and second fields in the direction opposite to the motionvector;

FIG. 12 is a view showing a result of shifting images according to theshifting method shown in FIG. 11;

FIG. 13 is a block diagram showing the structure of an image signalprocessing apparatus which rearranges the order of fields forming aunit-frame, with respect to inputted image signals, and then outputs thesignals to the CRT;

FIG. 14 is a view showing an example of the operation of the imagesignal processing apparatus which rearranges the order of fields forminga unit-frame and then outputs the signals;

FIG. 15 is a view for explaining an example of the operation of theimage signal processing apparatus shown in FIG. 14, where the order offields forming a unit-frame is rearranged;

FIG. 16 is a view showing a second example of the operation of the imagesignal processing apparatus which rearranges the order of fields forminga unit-frame and then outputs the signals;

FIG. 17 is a view showing a third example of the operation of the imagesignal processing apparatus which rearranges the order of fields forminga unit-frame and then outputs the signals; and

FIG. 18 is a view showing a fourth example of the operation of the imagesignal processing apparatus which rearranges the order of fields forminga unit-frame and then outputs the signals;

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in detailswith reference to the drawings.

The present invention is applied to an image signal processing apparatusbuilt in a television receiver according to PAL system (PhaseAlternation by Line).

An image signal processing apparatus 1 to which the present invention isapplied has a structure as shown in FIG. 5.

The image signal processing apparatus 1 has a first image memory 11, asecond image memory 12, a sequence detector 13, a motion vector detector14, an image shifter 15, a reverse image shifter 16, and a switch 17, asshown in FIG. 5.

The first image memory 11 is sequentially supplied with interlace imagesignals of, for example, 100 fields/second which are generated byperforming double-speed conversion on images subjected to telecineconversion and have a unit-frame formed of 4 fields.

The first image memory 11 stores the supplied image signals for everyframe, in units of fields. That is, the image signals are outputted fromthe first image memory 11 after one frame after the image signals weresupplied to the first image memory 11.

The second image memory 12 has the same internal structure as the firstimage memory 11 and stores the image signals supplied from the firstimage memory 11 for every one frame, in units of fields. That is, theimage signals are outputted from the second image memory 12 one frameafter the image signals were supplied to the second image memory 12,i.e., two frames after the image signals were supplied to the firstimage memory 11. The image signals stored in the second image memory 12are supplied to the motion vector detector 14.

The sequence detector 13 detects the image signals supplied to the firstimage memory 11 and the image signals outputted from the first imagememory 11, and compares image signal levels for every pixel, tocalculate a difference value between the supplied and outputted signals.That is, the sequence detector 13 compares the image signal levels foreach pixel at one single part of a screen, at cycles of frames. Thesequence detector 13 transmits the calculation result concerning thedifference value of the image signal levels to the image shifter 15 andthe reverse image shifter 16.

The motion vector detector 14 detects the image signals supplied to thefirst image memory 11 and the image signals outputted from the secondimage memory 12, and detects a motion vector based on, for example, theblock matching method. In this block matching method, the screen isdivided into blocks each consisting of predetermined pixels, and motionvectors are obtained by evaluating similarity in units of blocks. Themotion vector detector 14 transmits a motion vector detected for everypixel or for every block, to the image shifter 15 and the reverse imageshifter 16.

The image shifter 15 receives the result of comparing the pixel signallevels from the sequence detector 13. The image shifter 15 also receivesthe motion vector detected by the motion vector detector 14. Further,the image shifter 15 is supplied with image signals delayed by one framefrom the inputted image signals, from the first image memory 11. Theimage shifter 15 shifts each pixel position of the supplied imagesignals in the vector direction of the received motion vector within therange of the received motion vector.

The reverse image shifter 16 receives the result of comparing the pixelsignal levels from the sequence detector 13. The reverse image shifter16 receives the motion vector detected by the motion vector detector 14.Further, the reverse image shifter 16 is supplied with image signalsdelayed by one frame from the inputted image signals, from the firstimage memory 11. The reverse image shifter 16 shifts each pixel positionof the supplied image signals in the direction opposite to the receivedmotion vector. Note that the reverse image shifter 16 is applicable evenin the case where the reverse image shifter 16 is integrated with theimage shifter 15.

The image shifter 15 and reverse image shifter 16 supply the switch 17with those image signals that have pixel positions having been shiftedin units of fields. Based on the result of comparing pixel signal levelssupplied from sequence detector 13, the switch 17 selects necessaryimage signals in units of fields. The image signals selected by theswitch 17 are outputted to the CRT 2. The CRT 2 displays the imagesignals inputted from the switch 17, on the screen, and controlsdeflection of the image signals in horizontal and vertical directions,based on a horizontal/vertical deflection circuit not shown.

In some cases, a double-speed field conversion circuit 3 which performsdouble-speed conversion on the field frequency of image signals may beintegrated in the image signal processing apparatus 1. The double-speedfield conversion circuit 3 is integrated to prevent screen flickerdisturbance by improving the resolution. For example, a processing suchas interpolation is performed in the PAL system, to convert imagesignals having a field frequency of 50 Hz into image signals having adouble frequency which is 100 Hz.

The double-speed field conversion circuit 3 has an input terminal 31connected to the television receiver, a double-speed converter 32, and aframe memory 33, as shown in FIG. 5.

The double-speed converter 32 writes images signals after the telecineconversion, which are inputted through the input terminal 31 from thetelevision receiver, into the frame memory 33. The double-speedconverter 32 reads the image signals written into the frame memory 33,at a speed which is twice the writing speed. As a result, for example,the frequency of the image signals of 50 fields/second according to thePAL system is converted to a double frequency, so that image signals of100 fields/second can be generated. The double-speed converter 32supplies the image signal processing apparatus 1 with the image signalssubjected to the double-speed conversion.

FIGS. 6A and 6B show a relationship between each field and pixelpositions before and after the double-speed conversion in thedouble-speed field conversion circuit 3. In the figures, the abscissaaxis represents time and the ordinate axis represents the position ofeach pixel in the vertical direction.

The image signals before the double-speed conversion are interlace imagesignals of 50 fields/second according to the PAL system, and everyunit-field is formed of two fields, as shown in FIG. 6A.

On the other side, the image signals after the double-speed conversionare interlace image signals of 100 fields/second. Therefore, as shown inFIG. 6B, new two fields t₂′ and t₁′ are generated between fields t₁ andt₂. No fields are generated between fields t₂ and t₃ but new two fieldst₄′ and t₃′ are generated between fields t₃ and t₄. Therefore, in theimage signals, every unit-frame is formed of four fields.

In some cases, those newly generated fields t₁′, t₂′, . . . are obtainedby using a median filter or the like, supposing that each pixel value isan intermediate value among three pixels surrounding each pixel. Thenewly generated fields t₁′, t₂′, . . . have the same contents as thefields t₁, t₂, . . . , respectively. The newly generated fields t₁′,t₂′, . . . have the same contents as the fields t₁, t₂, . . . ,respectively. As a result of this, every unit-frame is formed of fourfields, so that the resolution can be improved by increasing the numberof screens per unit time. Accordingly, the screen flicker disturbancecan be suppressed.

Next, the operation of the image signal processing apparatus 1 accordingto the present invention will be described.

The image signal processing apparatus 1 is sequentially supplied withimage signals subjected to double-speed conversion after telecineconversion and consisting of unit-frames each formed of four fields,from the double-speed field conversion circuit 3. FIG. 7 shows arelationship between each field and an image position in case where animage moves in the horizontal direction of the image signal. In FIG. 7,the abscissa axis represents the position of the image in the horizontaldirection, and the ordinate axis represents time. Images alreadysubjected to the telecine conversion are supplied to the first imagememory 11 at a constant time cycle, in the order of fields t₁, t₂′, t₁′and t₂, and the images are all displayed on one equal position. As thefield shifts to t₃, the image shifts in the horizontal direction (to theright side), and the images are supplied to the first image memory 11 inthe order of fields t₃, t₄′, t₃′ and 4.

When, for example, the field t₃ is supplied to the first image memory 11(hereinafter referred to as a reference field), the field t₁ whichprecedes by two frames the reference field is outputted from the secondimage memory 12 (hereinafter referred to as a two-frame-delayed field).

The motion vector detector 14 detects a motion vector between thereference field and the two-frame-delayed field in units of pixels orblocks. In case of the example shown in FIG. 7, the vector direction ofthe motion vector is the horizontal direction (to the right side) withthe two-frame-delayed field taken as a reference, and has a vectorquantity of A. Similarly, when the reference field is the field t₅, thetwo-frame-delayed field is t₃ and the vector mount of the motion vectoris B. By repeating this procedure, the directions and quantities ofvectors can be sequentially obtained taking each two-frame-delayed fieldas a reference. The motion vector detector 14 sequentially transmits theobtained vector directions and quantities to the image shifter 15 andreverse image shifter 16.

The sequence detector 13 sequentially detects the reference fields andthose fields each of which precedes by one frame the reference fieldoutputted from the first image memory 11 (hereinafter referred to asone-frame-delayed field), and calculates difference values in pixelsignal levels at an equal pixel position.

More specifically, as shown in FIG. 8, the reference field t₁′ and theone-frame-delayed field t₁ form one single unit-frame, so that thedifference value in pixel signals levels, for example, at a pixelposition a is 0. Next, the field t₂ is supplied as the reference field,and then, the field t₂′ becomes the one-frame-delayed field. Therefore,the difference value in pixel signal levels at a pixel position a is 0,too.

Next, the field t₃ is supplied as the reference field, and then, theone-frame-delayed field is t₁′. Since both of these field respectivelyform parts of different unit-frames, the difference value in pixelsignal levels at the point a is not 0 (but will be 1 hereinafter). Next,t₄′ is supplied as the reference field, and then, the field t₂ becomesthe one-frame-delayed field, so that the difference value in pixelsignal levels at the point a is 1, too.

Further, t₃′ is supplied as the reference field, and then, theone-frame-delayed field is t₃. Since both of these fields form one equalunit-frame, the difference value in pixel signal levels at the point ais 0 again. This tendency applies to reference fields suppliedthereafter. The calculated difference values of “0011” repeat in thisorder at a cycle of four fields. Hence, it is possible to specifyrelationships of each field to preceding and following fields, bydetecting the sequence for every unit of four fields.

Where this tendency is observed with respect to the one-frame-delayedfields, the difference values are “0011” in the order from the firstfield of every unit-frame. Therefore, when the difference value “0” iscalculated at first, the one-frame-delayed field detected at this timeis specified as the first field of a unit-frame (hereinafter referred toas the first field), as shown in FIG. 8. When the difference value “0”continues, the one-frame-delayed field detected at this time isspecified as the second field. When 1 is calculated at first to be thedifference value, the one-frame-delayed field detected at this time isspecified as the third field. When the difference value “1” continues,the one-frame-delayed field detected at this time is specified as thefourth field.

The sequence detector 13 transmits the results of specifying therelationships of each field to preceding and following fields, to theimage shifter 15 and reverse image shifter 16.

The image shifter 15 and reverse image shifter 16 shift the positions ofdetected pixels of the supplied image signals, in the vector directions,based on the relationships of each field to preceding and followingfields specified by the sequence detector 13. Which of the first tofourth fields each field corresponds to has been found out before theimage signals are supplied to the image shifter 15. Therefore, thepositions of detected pixels can be shifted correctly and easily.

With respect to the shift direction of each field, the image signal isshifted in the direction opposite to the motion vector in each firstfield, and the image signals is shifted in the direction along themotion vector in each of the second and later fields, as indicated byblack arrows in FIG. 9. In the second and later fields, the shift amountis increased gradually from the second field within the vector quantityof each motion vector, so that the shift amount in the fourth field isthe greatest. That is, in the present invention, the fields are shiftedin the directions along motion vectors and in the opposite directions ofmotion vectors, balanced between each other, so that the shift amount issuppressed in the fourth field in which the shift amount is maximum, toreduce errors in detecting motion vectors.

The errors in detecting motion vectors mean those cases in which thedirections of the detected motion vectors are wrong, for example, whenan image includes motions in two directions in one single block (e.g.,an image of an object moves in the leftward direction while thebackground moves in the rightward direction). For example, in an exampleof motion correction in which the image signal in every field is shiftedonly in the vector direction of the motion vector, as indicated bydotted arrows in FIG. 9, the shift amount itself becomes excessive inthe fourth field. If the direction of a detected motion vector is wrong,the error appears emphasized on the screen because the image is movedgreatly in the fourth field.

Meanwhile, in the present invention in which images are shifted in thedirections along the motion vectors and in the opposite direction of themotion vectors, balanced among the respective fields, the shift amountin the fourth field can be suppressed to be small as shown in FIG. 9. Asa result of this, even if the direction of a detected motion vector iswrong when an image includes motions in two directions in one block,smooth motions can be realized without making this error conspicuous.

In the example shown in FIG. 9, the shift amount of each image can beincreased by 1/4 of the detected motion vector every time the fieldshifts after the second field, where the shift amount in the secondfield is 0. In this case, if the vector quantity is A, the shift amountin the second field is 0, the shift amount in the third field is A×1/4,and the shift amount in the fourth field is A×2/4. Further, in the firstfield in the next unit-frame, the shift amount can be set to 1/4 of themotion vector A. Likewise, if the motion vector in the next unit-frameis B, the shift amount in the second field can be set to 0, the shiftamount in the third field can be set to B×1/4, and the shift amount inthe fourth field can be set to B×2/4.

By thus shifting the images, the shift amount can be increased linearlywith respect to time, so that the motion of the image can be muchsmoother.

FIG. 10 shows a result of shifting an image throughout the fields. Theimage moves gradually in the horizontal direction as the field shifts toa later field. That is, the image shifter 15 can disperse a shift amountequivalent to a motion vector to respective fields. As a result of this,the image can be moved smoothly without moving greatly when the fourthfield shifts to the first field, compared with an image before theshifting.

Alternatively, the image shifter 15 can shift each image in thedirection opposite to the motion vector in the first and second fields,and in the direction along the motion vector in the third and laterfields, as shown in FIG. 11. In this case, in the first and secondfields, the image is shifted such that the shift amount decreasesgradually as the field shifts subsequently from the first field. In thethird and fourth fields, the shift amount is increased gradually withinthe vector quantity of the motion vector as the field shiftssubsequently from the third field, and is maximized in the fourth field.As a result of this, the images in the respective fields are shifted indifferent directions, like the example shown in FIG. 9, so that theshift amount per field can be suppressed and errors in detecting themotion vector can be reduced.

In the example shown in FIG. 11, the shift amount in the third field canbe set to 0, and the shift amount of each image can be increased by 1/4of the detected motion vector every time the field shifts after thethird field. In this case, if the vector quantity is A, the shift amountin the third field is 0, the image in the fourth field is shifted byA×1/4. In the first field in the next unit-frame, the shift amount isset to 2/4 of the motion vector A, and the shift amount in the secondfield is set to 1/4. Likewise, if the motion vector B in the nextunit-frame is B, the shift amount in the third field can be set to 0,and the shift amount in the fourth field can be set to B×1/4.

FIG. 12 shows a result of shifting the images as shown in FIG. 11. Alsoin this FIG. 12, each image is moved gradually in the horizontaldirection as the field shifts to a later field.

Further, in the image shifter 15, each image in the first to thirdfields can be shifted in the direction opposite to the motion vector,and the image in the fourth field can be shifted along the direction ofthe motion vector. In this case, each image is shifted such that theshift amount gradually decreases from the first field.

If the image signal processing apparatus 1 in which the double-speedfield conversion circuit 3 is integrated is built in the televisionreceiver, it is possible to eliminate discontinuity in motions which isspecific to image signals subjected to double-speed conversion aftertelecine conversion. That is, in a variety of cases including the casethat an image includes motions in two directions in one single block,and the like, the image signal processing apparatus 1 can improve theresolution by the double-speed field conversion circuit 3, suppress thescreen flicker disturbance, and more smoothen the motion of each image.

Therefore, remarkable advantages can be obtained by the image signalprocessing apparatus 1 not only in case of sole practical use but alsoin practical use integrated with the double-speed field conversioncircuit 3. In addition, version-up can be easily realized with respectto a television receiver which has already integrating the double-speedfield conversion circuit, if the image signal processing apparatus 1 isbuilt in later.

The image signal processing apparatus 1 according to the presentinvention is not limited to the embodiment described above. The presentinvention is applicable to an image signal processing apparatus 4 whichrearranges the order of fields forming every unit-frame of inputtedimage signals and then outputs the signals to the CRT 2. FIG. 13 showsan example of the block structure of the image signal processingapparatus 4. The same components as those of the foregoing image signalprocessing apparatus 1 will be denoted at identical reference symbols,and detailed explanation thereof will be omitted herefrom.

The image signal processing apparatus 4 has a first image memory 11, asecond image memory 12, a sequence detector 13, a motion vector 14, animage shifter 55, a reverse image shifter 56, and a switch 17.

The image shifter 55 receives results of comparing image signal levels,from the sequence detector 13. The image shifter 55 receives motionvectors detected by the motion vector 14. Further, the image sifter 55shifts the pixel positions of image signals supplied from the secondimage memory 12, within the ranges of the vector quantities of thereceived motion vectors, and in the vector directions of the motionvectors. That is, the image shifter 55 shifts those image signals thatare delayed by two frames from inputted image signals.

The reverse image shifter 56 receives the results of comparing pixelsignal levels, from the sequence detector 13. The reverse image shifter56 receives the motion vectors detected by the motion vector detector14. Further, the reverse image shifter 56 shifts the pixel positions ofimage signals supplied to the first image memory 12, within the rangesof the vector quantities of the received motion vectors and in thedirections opposite to the motion vectors. That is, the reverse imageshifter 56 shifts those image signals that are the same as the inputtedimage signals and therefore have a time difference by two frames fromthe image signals shifted by the image shifter 55. In some cases, thereverse image shifter 56 is constructed to be integrated with the imageshifter 55.

The image signals shifted by the image shifter 55 and the reverse imageshifter 56 are both inputted to the switch 17. The switch 17 selectsnecessary image signals in units of fields, based on the result ofcomparing the pixel signal levels supplied from the sequence detector13. The image signals selected by the switch 17 are outputted to the CRT2.

Next, the operation of the image signal processing apparatus 4 to whichthe present invention is applied will be described with reference toFIG. 14.

The image signal processing apparatus 4 is sequentially inputted withimage signals subjected to double-speed conversion after telecineconversion and consisting of unit-frames each formed of four fields,from the double-speed field conversion circuit 3. The image signalprocessing apparatus 4 specifies the first and second fields of thesupplied image signals, delays these fields, based on the second imagememory 12, and shifts the image signals in these fields in the vectordirections of the motion vectors. Further, the image signal processingapparatus 4 specifies the third to fourth fields of the supplied imagesignals, and shifts the image signals in these fields in the directionsopposite to the motion vectors, without delaying these fields.

The image signals supplied to the image signal processing apparatus 4are arranged orderly at a predetermined time cycle, in the order offields t₁′, t₂′, t₁′, and t₂. As the field shifts to t₃, the image movesto the position defined by a motion vector A, and the image signals aresupplied to the image signal processing apparatus 4, in the order offields t₃, t₄′, t₃′, and t₄. As the fields further shifts to t₅, theimage then moves to the position defined by a motion vector B, and theimage signals are supplied to the image signal processing apparatus 4,in the order of fields t₅, t₆′, t₅′, and t₆.

The motion vector detector 14 detects a motion vector at a cycle ofevery two frames, from the image signals inputted to the image signalprocessing apparatus 4. For example, when the field t₁ is outputted fromthe second image memory 12, the field t₃ which comes two frames behindthe field t₁ is supplied to the first image memory 11. Therefore, themotion vector detector 14 firstly obtains a motion vector between thefields t₁ and t₃.

Next, when the field t₂′ is outputted from the second image memory 12,the field t₄′ is supplied to the first image memory. Therefore, a motionvector is detected between the fields t₂′ and t₄′. That is, the motionvector detector 14 sequentially detects motion vectors in the order ofnumbers written in the parentheses shown in FIG. 14.

A motion vector is detected in a time band (1), and thereafter, theimage shifter 55 is inputted with the field t₁. The reverse imageshifter 56 is inputted with the field t₃. The image shifter 55 shiftsthe image signal in the field t₁ in the vector direction or outputs thisimage signal to the switch 17 with the shift amount set to 0. The imagesignal in the field t₃ inputted to the reverse image shifter 56 isdelayed by two frames and then shifted in the vector direction, thusperforming no processing.

Likewise, a motion vector is detected in a time band (2), andthereafter, the image shifter 55 is inputted with the field t₂′. Theimage shifter 55 shifts the image signal in this field t₂′ in the vectordirection, and then outputs the signal to the switch 17. The field t₄′inputted to the reverse image shifter 56 is delayed by two frames, andthereafter, the image signal is shifted in the vector direction, thusperforming no processing.

A motion vector is detected between the fields t₁′ and t₃′ in a timeband (3), and thereafter, the field t₁′ is inputted to the image shifter55. The reverse image shifter 56 is inputted with the field t₃′. In thiscase, the reverse image shifter 56 shifts the image signal in theinputted field t₃′, in the direction opposite to the motion vector. Notethat the field t₁′ need not be processed since the image thereof isshifted by the reverse image shifter 56.

Similarly, in a time band (4), the inputted field t₄ is shifted in thedirection opposite to the motion vector by the reverse image shifter 56.

Further, in a time band (5), a motion vector is detected between thefields t₃ and t₅, and thereafter, the image shifter 55 is inputted withthe field t₃. The reverse image shifter 56 is inputted with the fieldst₅. The image shifter shifts the image signal in the field t₃ in thevector direction or sets the shift amount to 0. Although this field t₃has once been inputted to the reverse image shifter 56, no processing isperformed by the reverse image shifter 56, so that one field might notbe shifted repeatedly.

Similarly, in a time band (6), the image signal in the inputted fieldt₄′ is shifted in the direction along the motion vector by the imageshifter 55.

As can be understood from the processing procedure as described above,the image signal processing apparatus 4 shifts alternately the imagesignals of the fields supplied to the image shifter 55 and the reverseimage shifter 56, after detecting a motion vector.

FIG. 15 shows a result of rearranging the fields in accordance with theshift amounts in the image signal processing apparatus 4. In FIG. 15, inthe fields forming a unit-frame (e.g., the fields t₃, t₄′, t₃′, and t₄),the order of the input image signals is changed from that of the inputimage signals shown in FIG. 14. This suggests that whichever fieldstarts shifting at first among the fields forming one unit-frame, oneequal result can be obtained.

That is, the image signal processing apparatus 4 is capable of much moresmoothening the images while suppressing the screen flicker disturbance,in images of wide variations such as a case where an image includesmotions in two directions, in one single block, like the image signalprocessing apparatus 1 described previously.

In the example shown in FIG. 15, the shift amounts of the images can bearranged such that the shift amount of the field t₁ is set to 0 and theshift amount of the field t₁′ is set to 1/4 of the vector quantity ofthe detected motion vector. Further, in the first field in the nextunit-frame, the shift amount can be set to 2/4 of the vector quantity A,and the shift amount in the second field can be set to 1/4 of the vectorquantity A. Likewise, if the motion vector in the next unit-frame is B,the shift amount of the third field can be set to 0, and the shiftamount of the fourth field can be set to B×1/4. As a result of this, theoutputted image signals are the same as the example of shifted imagesshown in FIG. 15, so that the shift amount can linearly increase inaccordance with time. Hence, motions of images can be much moresmoothened.

The rearrangement of the fields is not limited to the example shown inFIG. 15. It is possible to set freely the vector directions and thevector quantities in and by which the image signals are shifted in thefour fields forming one unit-frame (e.g., in the inputted image signalswhich are arranged in the order of fields t₃, t₄′, t₃′, and t₄).

For example, as shown in FIG. 16, it is possible to shift the imagesignals such that the outputted image signals are arranged in the orderof fields t₄, t₃, t₄′, and t₃′ in the horizontal direction. Further, itis possible to shift image signals such that the outputted image signalsare arranged in the order of fields t₃′, t₄, t₃, and t₄′ in thehorizontal direction, for example, as shown in FIG. 18.

In the examples shown in FIGS. 16 to 18, if the shift amounts areincreased and/or decreased in units of quarters of the vector quantity,the shift amount can be increased and/or decreased linearly inaccordance with time, so that motions of images are much more improved.

The above image signal processing apparatuses to which the presentinvention is applied are not limited to the case of application to atelevision receiver according to the PAL system. For example, thepresent invention is applicable to a television receiver inputted withinterlace image signals of 60 fields/second (30 unit-frames/second)according to NTSC (National TV System Committee). Alternatively, thepresent invention is applicable to a television receiver according toSECAM system.

Further, the image signal processing apparatuses according to thepresent invention are not limited to those built in television receiversbut may be built in signal converters connected to television receivers.

The present invention is not limited to the embodiment described abovewith reference to the drawings but it would be obvious to the persons inthe art that various modifications, substitutions, and equivalents ofthe present invention can be achieved without deviating from the scopeand the subject matter of the appended claims.

INDUSTRIAL APPLICABILITY

As has been described above, according to the image signal processingapparatus and method, image signals which are generated by performingdouble-speed conversion on images subjected to telecine conversion andconsist of unit-frames each formed of four fields are inputted, and therespective fields are specified on the basis of calculated differencevalues in pixel signal levels. The positions of detected pixels areshifted such that the pixel position in the first field thus specifiedis shifted in a direction opposite to a motion vector, the pixelposition in the fourth field also specified is shifted in the motionvector, and the pixel positions in the second and third fields alsospecified are shifted to be gradually closer to the pixel positionshifted in the fourth field as the fields come later from the firstfield.

As a result of this, the image signal processing apparatus and methodaccording to the present invention are capable of smoothening motions ofimages while suppressing screen flicker disturbance with respect toimages of wide variations, e.g., in the case that an image includesmotions in two directions in one single block.

1. An image signal processing apparatus inputted with an image signalwhich is generated by performing double-speed conversion on an imagesubjected to telecine conversion and which is formed of unit-frames eachincluding four fields of first and successive second to fourth fields,each of the unit-frame staring from the first field, comprising: asequence detector which calculates a difference value in signal levelbetween a detected pixel in a current field and a detected pixel at thesame position in a field which comes one frame behind the current field,with respect to the inputted image signal, and specifies each of thefields forming the unit-frame, based on the difference value; a motionvector detector which detects a motion vector for a field which comestwo frames behind the current field, with respect to the detected pixelin the current field; and an image controller which shifts the positionsof the detected pixels of the image signal within the fields specifiedby the sequence detector, respectively, in accordance with a vectorquantity of the detected motion vector, wherein the image controllershifts the detected pixel, with respect to the specified first field, ina direction opposite to the motion vector, the image controller shiftsthe detected pixel, with respect to the specified fourth field, in adirection along the motion vector, and the image controller shifts thedetected pixels, with respect to the specified second and third fields,so as to make the pixels gradually closer to the pixel position shiftedwith respect to the fourth field, in the consecutive order of the fieldsfrom the first field, in the direction along the motion vector or in thedirection opposite to the motion vector.
 2. The apparatus according toclaim 1, wherein the image controller sets a shift amount of the secondfield to
 0. 3. The apparatus according to claim 2, wherein every time alater field follows the second field, the shift amount is increased by1/4 of the vector quantity of the motion vector detected, and the shiftamount of the first field is set to 1/4 of the vector quantity of themotion vector based on a field which comes two frames before the currentfield.
 4. The apparatus according to claim 1, wherein the imagecontroller sets the shift amount of the third field to
 0. 5. Theapparatus according to claim 4, wherein the image controller sets theshift amount of the fourth field to 1/4 of the vector quantity of themotion vector detected, sets the shift amount of the first field to 2/4of the vector quantity of the motion vector based on the field whichcomes two frames before the current field, and sets the shift amount ofthe second field to 1/4 of the vector quantity of the motion vectorbased on the field which comes two frames before the current field. 6.The apparatus according to claim 1, wherein if the difference valuesequentially becomes 0, the sequence detector specifies the currentfield inputted earlier, as the first field.
 7. The apparatus accordingto claim 1, wherein the motion vector detector detects the motionvector, based on a block matching method, for every block including apredetermined number of pixels.
 8. The apparatus according to claim 1,wherein the inputted image signal is an interlace image signal accordingto PAL system.
 9. An image signal processing method comprising the stepsof: inputting an image signal which is generated by performingdouble-speed conversion on an image subjected to telecine conversion andwhich is formed of unit-frames each including four fields of first andsuccessive second to fourth fields, each of the unit-frame staring fromthe first field; specifying each of the fields forming the unit-frame,with respect to the inputted image signal, based on a difference valuecalculated in signal level between a detected pixel in a current fieldand a detected pixel at the same position in a field which comes oneframe behind the current field; detecting a motion vector for a fieldwhich comes two frames behind the current field, with respect to thedetected pixel in the current field; shifting the detected pixel, withrespect to the specified first field, in a direction opposite to themotion vector; shifting the detected pixel, with respect to thespecified fourth field, in a direction along the motion vector; andshifting the detected pixels, with respect to the specified second andthird fields, so as to make the pixels gradually closer to the pixelposition shifted with respect to the fourth field, in the consecutiveorder of the fields from the first field, in the direction along themotion vector or in the direction opposite to the motion vector.
 10. Themethod according to claim 9, wherein a shift amount of the second fieldis set to
 0. 11. The method according to claim 9, wherein every time alater field follows the second field, the shift amount is increased by1/4 of the vector quantity of the motion vector detected, and the shiftamount of the first field is set to 1/4 of the vector quantity of themotion vector based on a field which comes two frames before the currentfield.
 12. The method according to claim 9, wherein the shift amount ofthe third field is set to
 0. 13. The method according to claim 12,wherein the shift amount of the fourth field is set to 1/4 of the vectorquantity of the motion vector detected, the shift amount of the firstfield is set to 2/4 of the vector quantity of the motion vector based onthe field which comes two frames before the current field, and the shiftamount of the second field is set to 1/4 of the vector quantity of themotion vector based on the field which comes two frames before thecurrent field.
 14. The method according to claim 9, wherein if thedifference value sequentially becomes 0, specifying the current fieldinputted earlier, as the first field.
 15. The method according to claim9, wherein the motion vector is detected, based on a block matchingmethod, for every block including a predetermined number of pixels. 16.The method according to claim 9, wherein an interlace image signalaccording to PAL system having a field frequency converted to a doublefrequency of 100 fields/second from 50 fields/second is inputted as theimage signal.